Gas or vapor discharge tube



P 1937. H. J. SPANNER ET AL 2,092,363

GAS OR VAPOR DISCHARGE TUBE Filed NOV. 19, 1932 Patented Sept. 7, 1937 GAS OR VAPOR PATENT OFFICE DISCHARGE TUBE Hans Joachim Spanner and Werner Lucas, Berlin, Germany; said Spanner Lucas asslgnor to said Application November 19, 1932, Serial No. 643,502 In Germany November 21,. 1931 8 Claims.

This invention relates to arc-lamps which are used to produce visible and ultra-violet rays. According to their purpose these lamps are enclosed in envelopes of coloured or clear glass, or

of quartz etc. These lamps may be used for therapeutic radiation, or for vitaminization as well as for illumination and/or other purposes.

' Among main parts of the discharge tube are the electrodes, which in this case are adapted in to ,become incandescent without any additional heating medium. When used with alternating current, preferably at least two such electrodes are fitted in the tube, and they alternatively become cathode and anode. When direct current i5 is used, only one electrode of the self-heating type is necessary, and the anode can be made of some non-disintegrating material. It is advantageous to direct current to make the anode of larger dimensions than the cathode, according to 0 the different cathode and anode drops.

The electrodes consist of a metal, such as nickel, which reacts favourably to the activating materials, especially barium and compounds of barium caesium or compounds of caesium. In

'3); order to reduce the destructive effect of the are on the electrodes, these are made of layers of nickel-sheeting or cups, or of twisted nickel wires. By the use of this porous structure, itis possible to insert the activating materials to a suflicient 3:) depth in extremely narrow gaps and holes.

There are several factors which must be taken into consideration to ensure reliable working of the arc-lamp and to determine the manner in which it differs from those hitherto known. The

33 cathode must be capable of starting an are after a glow discharge in the gas filling, which for example and preferably for most purposes, consists of argon. 'To this end it consists in practice of a texture of thin wires or any other porous structure made of some metal which, by virtue of its chemical properties, will not prevent the emission of electrons. This fabric is coated with an activating material, as, for instance, a compound of barium, or, in the case of smaller loads,

'1', of caesium or rubidium, or with mixtures of these .and/or other emissive substances.

The activating process of an electrode of this kind is the most diflicult problem. In manufacture, care must be taken to see not only that the 50 pure metal is formed at the surface, but also that, for instance, some of the barium oxide or other' activating material is reduced to a suboxide, e. g. partially reduced by a high temperature treatment, and preferably, that an in- .55 timate combination of the barium etc., with the base body, e. g. nickel, is formed. To this end the core may be covered with a mixture of substances including compounds of an emissive substance, the whole chemical structure of which is unstable. Now experiments by us have shown that unstable sub-compounds of this kind are actually extremely suitable for the emission of electrons.

Such electrodes will be suitable for the production of a glow-discharge which afterwards turns into an are, if the electrodes are formed in such a manner that the final result is as described above.

Such electrodes and the process for their preparation are more fully described and claimed in the copending applications Serial No. 351,368,

filed March 30, 1929; Serial No. 387,986, filedfactors outlined above, 'WhichJcontain, for instance, the pressure 4 mms. of argon which we have'used for working with 220 volts and which forms an are at that potential, it will be seen that at 110 volts supply current a glowdischarge only will be formed and that no change of the glow-discharge into an arc will take place. The reason for this is that although the electrode is excited to emission by the auxiliary electrode, and electrons also travel to the other electrode and in so doing collide with gas atoms, nevertheless because of the low pressure, i. e. the relatively few atoms present, these collisions which bring about ionization do not occur to an extent great enough to cause an avalanche of ions, which is responsible for creation of an are. An insuflicient quantity of atoms from the moving electrons is hit in the course of their passage. The pressure of the gasmust therefore be raised, in order to increase the probability of collisions.

Each tube, according to its dimensions, displays a certain behaviour, which is also dependent on the pressure of the gas. Even when pressures are reached which are too low, or too high, then no discharge at all takes place. Even when pressures are reached which are suficient for the occurrence of a discharge, a glow-discharge sets in at first in the lower range without any formation of an are; as the pressure is increased, but not until shortly before the upper In view of the fact that use is made not of n interior. but of an exterior auxiliary electrode,-

such as, for instance, a conductive strip running along the wall, it has been found that especially in such case it is important that this conductive strip should cover as great a surface as possibleof the glass, envelope, say, one third of its surface; and, furthermore that relatively large surface should be brought as close as possible, to the activated parts of the electrode and should preferably surround same. The pole containers in which the electrodes are placed, should for best results be shaped in accordance with this aim. Also the exterior strip can consist of silver or chromium or chromium-plated metal, and act at the same time as reflector. The circular grooves which we place in front of the pole-containers enable the starting-strip to penetrate well into the discharge passage, and portions of the exterior strip should .therefore preferably lie along these circular grooves.

It is also of advantage if the activated surface of the electrodes is expanded in proportion to the non-activated surface.

The invention is illustrated by way of example in the accompanying drawing, in which Fig. 1 is a view, partly in section of a tube having a screw socket,

Fig. 1a is a separate view of an electrode contained in a said tube,

Fig. 2 is a longitudinal section of a tube having lead-in wires on bothends,

Fig. 3 is a longitudinal section of a tube forming a modification of the tube shown in Fig. 1,

Fig. 4 is a view of an entire illuminating device including a series resistance and a switch, and

Fig. 5 is a wiring diagram of a starting circuit, using an inductance and capacitance to produce the starting voltage.

Before entering into further details regarding the possible varations in shape and design of the radiating device, the process of preparation will be briefly described; the details given refer to a tube of the dimensions given in Fig. 1, which represents a tube in its actual size. If this tube is connected up to a supply current of volts and the initial current is adjusted to 5 amperes with the aid of a resistance, a current of 3.4 amperes sets in on conclusion of the period necessary for bringing the intensity up to the required pitch, that is to say, when high pressure has been formed by the mercury contained in the tubein accordance with the initial current set; and the tension measured on the tube itself rises from approximately 15 volts to 65 volts. The electrode I of this tube, shown in the separate drawing, Fig. 1a consists of a metal bow,hammered down to a thickness of about 1 mms. from 3 mm. nickel wire; on its front it has three coils consisting of 40 wires of pure nickel of 0.25 ms. diameter, comparatively closely interwoven and wound in such a manner that a short-circuit cannot occur between the three coils. The lead-in wire 3 consists in the case under consideration of tungsten wire, which is welded on to the metal bow, and sealed-in over the Corning glass 702 P. Dyrexglass, or uviol glass (Schott). The use of these glasses is more fully described and claimed in the applications Serial No. 51,390,v

filed November 25, 1935 and Serial No. 107,191, filed October.23, 1936. Before being sealed-in, the emitting part of the electrode is covered with as homogeneous a layer as possible of finc1y ground barium oxide, which has been 'worked up into a viscous mass in distilled water; I The electrode, when treated in this way, may not remain long in contactwith the and it should be sealed-in as quickly as possible.- If.the tube is connected to the pump piping, theglass-Jor now has-been of a pure white, runs and melts,

giving off oxygen and foreign gases, and aft/er cooling down it remains as a dark coating on the nickel wire, primarily as a sub-oxide on the surface. While the electrode is yet in this condition, it is not ready for use, and it would not start if charged with supply tension. To proceed with the process, the lighting-tube is now filled with argon at a pressure of from 4-10 mms Hg. column, and a somewhat higher tension-for instance, 220 volts-is connected up via a resistance. With the assistance of high frequency, the discharge can now be worked up. It is to be recommended that in the first moments the radiating device should not be loaded over 4 amperes. A large quantity of mercury has been filled in previously, and this now vaporizes as a result of the heating effects of the discharge, and takes over the carrying of the current. Shortly after the starting, theelectrodes still give off foreign gases, and this can be seen from the lively flickering which takes place. When the tube has got well burning, and is burning quietly without any more flickering, the strength of the current can be increased slowly up to about 7 amperes; but while this is being done care must continually be taken to see that there is always a suflicient mercury vapor pressure and that the quantity in the tube is not exhausted by condensation in the pump piping. .When the tube has now got burning well with this strong current, the lead to the high vacuum pump is opened once again and the gases are exhausted. The mercury arc, however, continues to burn quietly. The whole tube is now heated up by means of a burner or an electric furnace, the latter being better as it allows of continuous observation of the discharge; during this procedure, care must be taken to prevent the mercury vapor pressure becoming too high and the discharge interrupting itself. As the supply of mercury diminishes, the pressure of the vapor drops more and more, and this can be seen from the swelling of the discharge. Shortly before the whole mercury has evaporated from the tube, the supply of current must be cut off and the tube heated for a while, pumping being carried out at the same time. The surface of the activated parts of the structure-electrode has now assumed a dull metallic appearance, as owing to the passage of the current from the nickel into the sub-oxide layer, nickel compounds and alloys, as well as free barium, have formed. The tube is now. filled a second time with mercury and rare gas and treated as described above, except for the fact that one now manages on asupply tension of 110 volts; otherwise the, figures given above for current are adhered to. After coolingdown. a starting-strip-made, for instance, of a colloidal suspension of graphite in water and the like so called aquadagis provisionally fitted to the tube; this'covers at least one third of the outer surface of the tube; it is connected to one electrode, and is led up as close as possible to the other activated structure of the electrode and surrounds or envelopes it. Starting strips of this kind are broadly described and claimed in our 10 copcnding application Serial No. 107,191, filed October 23, 1936, also in the copending application of Edmund Germer, SerialNo. 500,346, filed December 5, 1930. If some mercury is now introduced into the tube, as also, for instance, some 5 argon at a pressure of approximately mms., after the first few starts the tubewill start of ,itself when connection i made with the supply current, if the assistance of high frequency is.

made use of, providing that the strength of the starting current is not too'low. If this be too low, a glow-discharge sets in, which is very damaging to the electrodes, and should therefore be avoided under all. circumstances. Before sealing-off, it is as well to raise the pressure of r the gas somewhat, as during the first part of the action rare gas is also taken up by the metal parts.

It is particularly advantageous to furnish the tube with a double pumping-tip 6, that is to say,

a piece of tube is left projecting beyond the groove intended for the final sealing-off, and the first sealing-off is carried out on this projecting piece of tube. In this way the quantity of mercury in the lighting-tube can be so limited that when the device is working, the mercury can only produce a certain vapor-pressure, which does not allow of the discharge interrupting itself as a result of too great an increase in pressure, that is, of too great a current load. To

' 40 carry out this evening-up. mercury is distilled into the lighting-tube whilst the normal working load is kept up in the latter; sufficient mercury is distilled from the pumping-tip into the lighting-tube to secure the desired potential drop, and it is then sealed-off. The above process is described for a radiating device filled with mercury and argon; it goes without saying, however, that 1 other elements can be used as well; for instance,

to obtain special lighting-effects, cadmium or even sodium can be distilled as well as the mercury. If the quantity of sodium is extremely small, the use of special sodium-proof glasses can even be omitted. The evening-up described can also be carried out in the case of these mix tures, and this can be done to advantage in such a manner that each individual filling component is limited in quantity, so that it forms a definite partial pressure of the total pressure.

Such mixed fillings are more fully described 00 and claimed in the co-pending application, Se-

rial No. 397,428, filed October 4, 1929, and Serial No. 744,206, filed September 15, 1934, and the limited dosage of metal in the copending application, Serial No. 558,148, file'd August 19, 1931.

It is of great importance for the formation of sure burners in the high pressure burners. For instance. a cadmium amalgam burner was unable to perform successful work, as the mixture separated within a. short while, the cadmium was deposited on the cooler spots, and finally almost r nothing but mercury lines occurred. The pumptip, in particular, has a harmful effect in this connection. Care must therefore be taken-to see that it is made as small as possible and preferably is placed in the neighbourhood of the hotm test place. Fig. 2 shows an example'of the shape for two different types of electrodes. 1 is the one already described above, and I0 is an electrode consisting of several nickel cups layered one inside the other. Thebest shape to be aimed 5 at is clearly shown in the drawing. The pump tip 6 can be given a cap or capsule of asbestos II. By making the glass envelope thicker or thinner, one can also affect the temperature, so that the minimum temperature required can be reached, :n or, as the case may be, exceeded, even at the coldest spot in the tube. For it is only when this is achieved that a regulation of the quantity of mercury can have favourable results. It is of advantage that the length of the tube should be adjusted to suit the terminal voltage which was set, and the supply current tension; this should be done in such a way that the economy will be as large as possible for the working figures given above. The most favourable length between electrodes for 110 volts line voltage and volts for the tube, exclusive of its ballasting impedance is 7 ems.

The proportioning of the tube, however, is claimed specifically in the copending application, Serial No. 744,206, filed September 15, 1934.

A series resistance of incandescent lamps has proved to be of especial value for ensuring starting; of their very nature, the filaments of these lamps only offer a slight resistance to the current '1 in the first few moments, and this excites the electrodes strongly to emission.

This is described more fully and claimed in the application Serial No. 107,190, filed October 23, 1936. 45

Various adjuncts can be used for tubes which do not start with use of normal supply tension,

.as a result of their dimensions and filling. For

instance, the connecting-up shocks in non-ohmic electrical impedances can be made to act on the 50 electrodes, on an auxiliary electrode or the wallstrip, to ionize the discharge route. Or else resonance-circuits can be built, by placing a chokecoil in series, and a condenser in parallel, with the discharge tube, so that overbalanced reson- 55 ances (Kippresonancen"). are formed with the supply tension, which cause the discharge to set in. Strong effect is also achieved by switching on and off the condenser which is in parallel.

In the diagram shown in Fig. 5, 2| is the lamp, 60 connected to the source of alternating voltage 25, through the inductance 24. In parallel with the lamp 2|, is a capacitor 23, which can be connected or disconnected by means of the switch 22. This is described and claimed in our copending application Serial No. 107,191, filed October 23, 1936. For medical irradiation purposes the radiation device can be fitted with a casing which allows of the. passage of ultra-violet rays, for instance, quartz or uviol-glass; and if necessary an incandescent lamp placed in series can be enclosed in a casing allowing of the passage of ultra-violet rays, and its filaments be regulated in size accordingly. Since, however, the current which flows through the tube at the first moment exceeds the final current by two or three times, it is to be recommended that the ballast incandescent lamp be either fitted with two filaments, in such a way that connection is first made to the one and one then switches over to the other; or else that this ballast incandescent lamp be not placed in circuit in place of another resistance until after starting has taken place, and this could be accomplished, for instance, by means of a bi-metal mechanism. An iron-hydrogen resistance in series can also prevent overloading.

This is described and claimed in the copending application, Serial No. 107,190, filed October 23, 1936.

For actual technical use it is of advantage to fit the lighting-tubes in sockets in such a manner that they fit standard incandescent lamps or strip-lamps. With this end in view, a type of socket 8 can be selected, as shown in Fig. 1. In this case the conductive strip 4 is made of a solid metal sheeting or wire, which is arranged along a graphite liner 4a applied in the outer tube surface and represents at the same time the lead to the other electrode la. The lighting tube is secured to a pole container by means of a slotted metal tube 1, which is fitted to the outer contours of the pole container and fastened to the latter by being compressed by surrounding wires la. The metal tube 1 continues into an Edison screw-thread, and it is fitted with some apertures 9, for the purpose of better cooling by convention and diminishing of the conductance of heat. The conductive strip terminates at this metal tube, and is riveted thereon.

Another very advantageous type is one in which both leads to the electrodes are sealedin on the same side. See Fig. 3. One of the leads, i2, is surrounded within the interior of the tube 2 by an insulating layer l3, which in the drawing is a glass tube, to do away with the impact of the discharge. A metal band It is fitted over this glass tube, and also, if necessary, an exterior layer l5, to make starting easier.

These particular constructional features are described and claimed in our copending application, Serial No. 107,189, filed October 23, 1936.

According to Fig. 4 an entire illuminating body is composed of two radiating tubes 2, 2a, adapted to start on different voltages and connected in parallel and of a series resistance constructed as an incandescent lamp l6 having two metallic filaments 16a, 16b of a larger and a smaller electric resistance respectively. All said members are united on a frame I! adapted to be suspended on a ceiling and containing an automatic switch I8 for inserting either of said filaments into the current circuit of the tubes. For this purpose, said switch It consists of a bimetal strip which in cold state touches a contact Ma and inserts the filament lGa, whereas, after the generation of a certain heat by the tubes, the strip l8 touches a second contact I8b' and inserts the filament [6b having a smaller resistance. These features are particularly claimed in a copending application Serial No. 107,190, filed October 23, 1936.

In this combination a certain drawback is also eliminated which arises from the circumstance that lighting tubes of the described high-pressure type do not start again at once in hot state after being cut out, owing to the too high vapor pressure. This unhappy state of affairs is overcome, by the described combination of two (or more) lighting-tubes in parallel and connecting them to a common resistance in series. In this case, when current is turned on, the tube with the lowest starting tension starts first and prevents the other tube from starting at all. If the apparatus is cut out while high pressure is still prevailing in said first tube, and then turned on again immediately, the other cold tube now starts in place of the hot tube, so that in practice a start is always secured.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:-

1. The method of supplying an electrical discharge device having an envelope and electrodes with an accurately measured amount of a vapor which comprises starting a discharge in the device between the electrodes thereof slowly pass ing said vapor into the envelope, meanwhile measuring the electrical character of the discharge to determine the pressure of the vapor in the device while maintaining the envelope at a temperature above that at which the vapor would condense, and sealing oif the envelope when the discharge shows the desired electrical character.

2. The method of'supplying an electrical discharge device having an envelope and electrodes with an accurately measured amount of vapor which comprises sealing oif the envelope and a connecting chamber with an excess of the vaporizable material therein, heating the envelope to a temperature at which the vapor does not condense, gradually vaporizing the vaporizable material, and when the desired amount of vapor is in said envelope, segregating the residue of the vaporizable material in said connecting chamber rable part of the envelope, passing a discharge through the vapors and determining the amount of vapors present in the envelope by measuring the character of the discharge, and, when the character of the discharge shows the desired amount of vapor, sealing olf said separable part of the envelope.

4. The method as defined in claim 3 in which the exhausting connection is first sealed off at a substantial distance from the main body of the envelope, and a portion of the exhausting connection serves as the separable part of the envelope.

5. The method as defined in claim 3 in which a relatively thin walled constriction is formed in the exhausting connection where it enters the main body of the envelope, the exhausting connection is first sealed off at a substantial distance from said constriction and the intervening length of said connection used as the separable part of the envelope, and the separation is effected by fusing said thin walled constriction, whereby sealing-oil may be effected before substantial heating of that part of said connection in which the unvaporized residue is contained.

6. A vapor arc tube adapted to operate at high temperature at which all of the vaporizable filling is evaporated comprising an envelope having a sealing tip extending therefrom a filling of a vapor which condenses substantially above atmospheric temperatures and insulation over said tip to prevent its acting as a cooling fin to condense said vapor.

7. The combination of a vapor lamp, the operating pressure of which results from vaporization of a filling material by heat generated in the discharge and the envelope of which has a sealed off pumping tip which forms a small cavity on the inside thereof, and means for limiting heat dissipation from the envelope at said pumping tip whereby to counteract the tendency of said cavity to collect the filling material by condensation therein.

8. A gaseous discharge device which comprises spaced solid electrodes at least one of which is an activated self-heating cathode adapted to start a glow discharge and after an initial heating-up to act as an arcing cathode, an envelope enclosing the electrodes and the discharge path between themand being constricted in a portion around the discharge path near said cathode, and a conductive capacity member closely surrounding said constricted portion of the envelope and connected to the opposite electrode whereby to facilitate the starting of the glow discharge and its conversion to an arc.

HANS JOACHIIJVI SPANNER. WERNER LUCAS. 

